In the past two decades, the problem of soil contamination has been recognized as being pronounced, extensive and acute; both in the United States and abroad. Clean-up of both accidentally and intentionally contaminated soil has been mandated by federal, state, and local governments. The complexity of the task of soil remediation is compounded by the wide variation among contaminated sites. It cannot be guaranteed that any two clean-up sites will contain soil having the same characteristics; be exposed to similar climatic or geological conditions; or even have similar chemical contaminants present at even roughly the same concentrations. Wide variations can occur from site to site or even from location to location within the same clean-up site.
Thus the methodology for each clean-up effort must be specifically designed to meet the conditions found at the given site. Various processing methods implemented in the past have met with limited success. Volatile or volatilizable contaminants can be removed by a variety of reactive or evaporative processes. These processes generally entail the use of absorbent and/or oxidizing reactant materials which react with volatile or volatilizable organics to form reaction by-products which are more environmentally acceptable than the original contaminants. Such systems generally entail heating the soil matrix or subjecting it to other physical procedures to volatilize the contaminants to remove them from the soil matrix.
Many chemical contaminants are not readily volatilizable and therefore are not amenable to the reactive and/or evaporative processes as previously described. These contaminants include, but are not limited to halogenated aliphatics and various substituted and non-substituted poly-and mono-aromatic hydrocarbons; for example, polyhalogenated biphenyls and the like. Irradiation of contaminated solid material such as soil has been proposed as a method for reducing certain specific contaminants; for example polyhalogenated biphenyls such as PBB and PCB. However, such procedures are costly and time consuming. Such treatment methods are of limited use for use in soil matrices containing high concentrations of a wide variety of contaminants.
Extraction processes have been proposed to remove chemical contaminants from soil and sludge. Such methods generally involve contacting water wet soil/sludge with suitable water-insoluble solvents in which the chemical contaminants are preferentially soluble. The solvent containing the contaminants are separated from the solid after which the solvent and contaminants may then be separated from one another and a suitable post-treatment process.
Because no universally effective remediation method has been proposed, on-site soil remediation has been essentially impossible in many cases. Clean-up and remediation efforts up to the present have concentrated on removal of contaminated soil from the site to either secure containment landfills or to incineration facilities. This is both expensive and sacrifices productive topsoil which, if remediated, could possibly support vegetative growth.
It would be highly desirable to provide a remediation method which could be employed effectively with a variety of different contaminated matrices such as water, soil, bio-solids, and the like to remove a variety of classes of chemical contaminants. It is also desirable to provide a process in which chemical contaminants, particularly any which may remain in the soil as post-treatment residue are rendered amenable to further chemical, biological or environmental degradation. It is also desirable that the contaminant removal process be one which can be accomplished in a continuous manner at or near the clean-up site. Furthermore it is desirable that the remediation process be one which is capable of reducing the level of contaminants present in various matrices, particularly in soil to a level below that which is mandated in the applicable environmental regulations, with reduction in contaminant concentrations to levels below current detection limits being highly desirable.